biggest tires with the 2.9, gearing

[feellnfroggy]

His clutch may be slippig, or he has a different gearing inside his trans, dont ask me how. But I can educatedly guess that maybe he meant 4th gear, even with 5.13's I dont see the 2.9 having the torque to push 37's 70 mph.

 

[The Jester Race]

His clutch may be slippig, or he has a different gearing inside his trans, dont ask me how. But I can educatedly guess that maybe he meant 4th gear, even with 5.13's I dont see the 2.9 having the torque to push 37's 70 mph.

It'll do it but the engine is spinning pretty high(about 4000). I took the GPS out and tried to get a picture of speed and RPM. You have to take my word for it that it is in 5th. I can't get a picture of the Tach, GPS and shifter while driving. There was a head stiffwind and it would not get up to 70mph or 4K in any gear.
[Jeremy Clarkson]I need more POWER!!![/Jeremy Clarkson]

I don't know if you can see that but it says 64mph @ 2900RPM and it is in 5th.

-Jester

 

[lethal-threat-b288]

33"s 3.73"s just fine in 4low and ok in 2wd in mud. Street driving is average with 18 miles per gallon

 

[tmaxxman]

i have 2.9 with 410 and 33s is that good or bad ????

 

[88Bronco2EB]

Math

I found a formula on some 4x4 site(can't remember the name) but it will give you your RPM at a given speed depending on what gears and tire size you run.

here it it!!

speed x gear ratio x 336 / tire size

I'm not sure were the 336 comes from it is just part of the formula, and the gear ratio would be your diff gears in a 1:1 ratio or 4th gear in a manual, 3rd gear in an auto. But you could just multiply your diff gears by your over drive gear ratio.

Ex. (60mph)

60 x 3.73 x 336 = 75,196.8

75,196.8 / 27 = 2,785 RPM

This would be my RPMs in 3rd gear with stock tires NOT over drive

Ex. (60mph in OD) Diff gears x OD gear ratio in A4LD auto trans

3.73 x 0.75 = 2.7975

60 x 2.7975 x 336 = 56,397.6

56,397.6 / 27 = 2,088.8 RPM

I think its pretty damn cool

 

[rusty70f100]

I'm running 235/75R15 tires (about 29") with 3.45 gears, and a M5OD. To tell the truth, that's probably too big of tire for those gears. Around town is fine, and highway is usually fine, depending on the steepness of the hill and the direction and speed of the wind. Freeway can really knock the speed back down in OD if the wind is wrong. Of course, 4th gear solves all these problems.

I keep telling people I'm going to put a big sail on top of it.

 

[TexCaliBII]

88BII,
That is neat. I run 30s/3.73/A4LD and the tach readings are pretty close from the formulae to what I see in the truck.

Jester,
I see your anti-lock light is on too, in the clouds even.... Cool

 

[feellnfroggy]

Its been my experience that 5th gear My tach usually moves about 200 rpms for a 15-20 mph change, (thats not exact just making a point how little it moves for big speed changes) You tires are alot larger than mine meaning your rpms should change less than mine for the same speed increase. Is it possible you tach needle is jumping, or your speedo needle is binding at some point, 2900 a 64 is believable, without a doubt. But it shouldnt jump that high in rpms for an 6 mph difference. I really think something is slipping.

 

[The Jester Race]

Its been my experience that 5th gear My tach usually moves about 200 rpms for a 15-20 mph change, (thats not exact just making a point how little it moves for big speed changes) You tires are alot larger than mine meaning your rpms should change less than mine for the same speed increase. Is it possible you tach needle is jumping, or your speedo needle is binding at some point, 2900 a 64 is believable, without a doubt. But it shouldnt jump that high in rpms for an 6 mph difference. I really think something is slipping.

Keep in mind my truck is not stock. Full width SAS, ~8" lift, 37" tires, and a tired old 2.9 with 186,xxx miles on it. A much larger profile. Wind resistance plays a big part.
It is possible something is slipping but I do think I'm closer to 4K @ 70 then you think I am.

My truck.

Back on topic, 5.13's with 37"s with the 2.9 is very drivable, just don't expect to be in a hurry anywhere.

-Jester

 

[Hahnsb2]

It is possible something is slipping but I do think I'm closer to 4K @ 70 then you think I am.

You'd be better off if you believed the basic math.
Run the number yourself.

http://pitbulltires.com/calculate.php

 

[The Jester Race]

You'd be better off if you believed the basic math.
Run the number yourself.

http://pitbulltires.com/calculate.php

I agree with you the numbers say I am full of shit. But in the real world the numbers are wrong. They do not account for an increase in weight, increase in rolling resistance, increase in wind profile, or the lack of power of the 2.9.

My offer still stands, come on down and drive my truck, and see for your self.

-Jester

 

[Hahnsb2]

I agree with you the numbers say I am full of shit. But in the real world the numbers are wrong. They do not account for an increase in weight, increase in rolling resistance, increase in wind profile, or the lack of power of the 2.9.

My offer still stands, come on down and drive my truck, and see for your self.

-Jester

Dude, wind resistance, weight, ect have zero to do with how many gear teeth are meshing together with a solid connection (a non slipping clutch) or how big the tires are. These are constants, increased rolling resistance doesn't change gear ratios and tire size. If you wanna debate this with an automatic that doesn't have a lock-up converter you may have a leg to stand on.

 

[feellnfroggy]

Hes right, the weight and resistance all have to do with the efficiency of your cylinder burn, the mechanicals are still solid material physics. But like I said I in no way doubt that you hitting 4k at 70, Im just really curious as to why if your pushing 29k at 64.


Have we jacked this thread or what? LOL, I apologize for my part in that.
Come to think of it the OP jacked his own thread, now thats funny.

 

[The Jester Race]

Dude, wind resistance, weight, ect have zero to do with how many gear teeth are meshing together with a solid connection (a non slipping clutch) or how big the tires are. These are constants, increased rolling resistance doesn't change gear ratios and tire size. If you wanna debate this with an automatic that doesn't have a lock-up converter you may have a leg to stand on.

You are too far gone. You have it set in your mind that I am full of shit, and thats fine. I am done arguing.

-Jester

 

[Hahnsb2]

You are too far gone. You have it set in your mind that I am full of shit, and thats fine. I am done arguing.

-Jester

Damn me and how I'm set in my ways of physics, math, and facts

Never said you were full of shit, but your tach is.